Leptospira is a genus of bacteria which is a member of the Spirochetes family. Other members of this family are Borrelia and Treponema. All three genuses are characterized by mobility, and a helical shape. All members of the family cause disease in animals, including humans, livestock, domesticated animals, and wild animals. For example, Borrelia is the causative agent for Lyme disease. Other diseases caused by Spirochetes include relapsing fever, syphilis and yaws.
Leptospira genus consists of a genetically diverse group of 12 species, eight of which are pathogenic, and four of which are non-pathogenic, and saprophytic. See Faine, et al., Leptospira and Leptospirosis (2nd edition, 1999, Melbourne, Australia, MediSci); Farr, Clin. Infect. Dis 21:1–8 (1995). Levett, Clin. Microbiol Rev. 14:296–326 (2001), incorporated by reference. There are over 200 known pathogenic serovars of Leptospira. It is hypothesized that structural heterogeneity in lypopolysacchacide structure accounts for this. See, Levett, supra.
Leptospirosis, the disease caused by Leptospira, is zoonotic. Transmission to humans results from contact with domestic or wild animal reservoirs, or via contact with animal urine. Infected individuals show a wide spectrum of clinical manifestations in the early phases of the illness including fever, headache, chills and severe myalgia. In 5–15% of the clinical infections, severe multisystem complications result, including jaundice, renal failure and hemorrhaging. See Farr, supra, Faine, et al., supra. Severe leptospirosis has a mortality rate of 5–40%.
There is a large spectrum of animal species which serve as reservoirs for the bacteria. As a result, human leptospirosis is found throughout the world, and is considered to be the most widespread zoonotic disease. High risk groups include military personnel, farmers, miners, sewage and waste removal workers, veterinarians and abattoir workers. See, in this regard, Levett, supra, Faine, et al., supra. New patterns of transmission of the disease have emerged; however, emphasizing the public health issues associated with this disease. In “developed” countries outbreaks have been associated with recreational diseases, such as white water rafters in Costa Rica, and sporting events involving extensive outdoor activity, such as triathlons and “Eco-challenges.” See, e.g., Levett supra; Jackson, Pediatr. Infect. Dis. J 12:48–54 (1993); Center For Disease Control and Prevention: Outbreak of leptospirosis among white water rafters in Costa Rica (1997); Update: Leptospirosis and Unexplained Acute febrile illness among athletes participating in triathlons: Illinois and Wisconsin (1998). Update: Outbreak of Acute Illness Among Athletes Participating in Eco-Challenge—Sahah 2000—Borneo, Malaysia (2000). Underlying conditions associated with poverty have led to large, urban, epidemics of leptospirosis in Brazil and other countries, resulting in high mortality rates. See Lomor, et al., Infect. Dis. Clin. North Am 14:23–39 (2000); Ko, et al., Lancet 354:820–5 (1999).
Leptospirosis is a major issue in agriculture as well, due to its association with livestock and domestic animals. Among the manifestations of animal leptospirosis are spontaneous abortions, still births, infertility, failure to thrive, reduced milk production, and high fatality rates in diverse species such as cows, pigs, sheep, goats, horses and dogs. See Faine, et al., supra. Other manifestations of the disease are chronic infection, and shedding of pathogenic leptospires. Standard approaches to controlling this include international and national quarantines in the animal husbandry industry, with negative economic ramifications.
Clearly, there is a need to control leptospirosis; however, efforts have been hindered due to a lack of effective approaches. Long term survival of pathogenic leptospires in soil and water, as well as the abundance of animal reservoirs support long term survival of the pathogen so eradication is not a viable option. Hence, efforts have turned to approaches based upon vaccines.
Currently, available vaccines are based upon inactivated whole cell, or membrane preparations of pathogenic bacteria. These appear to induce protective responses via antibody induction. See Levett, supra, Faine, et al, supra. These vaccines do not produce long term protection against infection, and they do not confer cross protective immunity against serovars not included in the vaccines used. The number of serovars possible, and the cost of multicomponent serovar vaccines have thwarted development in this area.
A key mechanism in the pathogenesis of leptospirosis, as in other spirochetal diseases (such as Lyme disease and syphilis), is the ability of the pathogen to disseminate widely in the host during the early stage of infection. See Faine, et al., supra. It is presumed that surface associated leptospiral proteins, mediate interactions which facilitate entry and dissemination through host tissues. Virulence factors associated with the surface of the bacteria serve as vaccine candidates, in that any immune or other protective response would block dissemination in the host. Another important aspect of surface associated proteins is that they are, literally, “surface-associated,” rendering them accessible to immune attack. Protective mechanisms associated with such surface associated proteins include antibody-dependent phagacytosis, and complement-mediated killing.
It would be desirable to have pure, or substantially pure Leptospira surface associated proteins available. Production of such proteins, in recombinant form, for example is cost effective, and provides a method to screen proteins to determine sub-unit or epitopic fragment based vaccines. Further, availability of recombinant proteins permits one to determine which proteins are conserved, especially among different pathogenic Leptospira, to determine which are the most suitable, cross-serovar vaccines.
There have been difficulties in identifying surface associated Leptospira proteins. using conventional biochemical and molecular biological methods. The genome of the spirochete Borrelia burgdorferi has been analyzed, and more than 100 surface associated lepoproteins were identified. The large size of the Leptospira genome (−4.6 Mb), and its complex life cycle suggest that a far greater number of surface associated proteins will be found. Using standard membrane extraction, isolation, and purification techniques, less than 10 Leptospira surface associated proteins have been identified and characterized. See Haake, et al., Infect. Immun 66:1579–1587 (1998); Haake, et al., Infect. Immun. 6572–82 (1999); Haake, et al., Infect. Immun 68:2276–2285 (2000); Shang, et al., Infect. Immun 63:3174–3181 (1995); Shang et al., Infect. Immun 64:2232–30 (1996). Also see U.S. Pat. Nos. 5,091,301; 5,643,754; 5,638,757; 5,824,321; 6,140,083; 6,262,235; 6,306,623; and 6,308,641. All of these articles and patents are incorporated by reference. While Haake, et al., Infect. Immun 67:6572–82 (1999), describe immunization with recombinant protein L1pL32, OmpL1 and L1pL41 but, the response was not complete. None of these reference identify virulence associated proteins.
As has been pointed out, supra, the Leptospira genome is large. As a result, technical difficulties have prevented meaningful results in identifying surface associated proteins; however, the emerging field of bioinformatics has placed extremely powerful and valuable tools in the hands of those involved in Leptospiral research.
Via application of the techniques described supra, the inventors have discovered further Leptospira surface associated proteins useful in vaccine production, as well as in production of diagnostic kits for use in determining presence, onset, or decrease in Leptospiral infection. These, and other aspects of the invention will be clear from the disclosure which follows.